The Beryl itself is available as the Radom Archer.. I think it's still being imported. There are some differences between the Archer and mil Beryl, and I don't believe anybody sells the Radom STANAG adapter.
If you're asking about the Beryl mags, you can buy these in the US, e.g. from Robert RTG Parts, and some sellers on auction sites. These conform to the Polish/Russian/Bulgarian pattern.
This is the Radom STANAG adapter which supposedly is available in some shape or form for the Beryl/Archer, but never heard of anyone in the US getting it. I don't know what if any modifications had to be made to the standard magwell/trunnion for the Radom adapter.
The US-made mag well conversions do require a bit of milling on the trunnion. I wish I had some machining experience, because just inserting a Pmag into my Saiga .223, I can see how it could potentially be done without trunnion modification.